Sebastes schlegeli is an important fish species to represent domestic marine aquaculture together with an olive flounder in Korea, and is an ovoviviparous fish species in which the body and fins are a brown color and the stomach is a gray color. The Sebastes schlegeli lives in a reef area of 10 to 100 m in depth and inhabits the northwest Pacific region of the Korean coast, Japan and China, and the like. At the beginning of the cultivation, an amount of sea surface fishery was larger than that of aquaculture production. However, since the late 1990s, the amount of aquaculture production has increased sharply, and the production amount increased to 35,564 tons in 2007 and accounted for 32.5% of total aquaculture production in 2013. However, since then, a production rate has slightly decreased, and the production amount was 18,774 tons in 2015, which accounted for about 22% of the aquaculture production in Korea (KOSIS, 2016).
As described above, the Sebastes schlegeli, has an important position in view aquaculture species; however, Sebastes schlegeli produced by the farms are dying due to frequent diseases over the course of the year and rapid changes in the breeding environment. Flexibacter, Streptococcus, Vibrio, and the like, have been reported as bacteria that infect the Sebastes schlegeli, and infection of red sea bream irido virus (RSIV), viral hemorrhagic septicaemia virus (VHSV), nervous necrosis virus (NNV), and Lymphocystis have been reported as viral diseases. Infection of Microcotyle, Epitheliocystis, Benedenia, Trichodina, Scutica and Caligus, and the like, as a parasite has been reported.
Recently, a Philometridae nematode parasitic disease on the epithelium such as fins, cephalus, or the like, of the Sebastes schlegeli, has been reported. Particularly, the present inventors have identified parasites that infect the Sebastes schlegeli at a molecular biological level by targeting 18S rRNA and COI (Cytochrome c oxidase subunit I) gene, and identified morphologically up to a species classification level, and as a result, finally confirmed the parasite as the Clavinema mariae. The Clavinema mariae was first isolated in the fins of a Pleuronectes schrenki in 1930 and was reported as Philometra mariae at that time. Machida later found the parasite in the fins and operculum of right-eyed flounder and Limanda yokohamae, and asserted to reclassify the parasite as Clavinema genus, and it was reclassified as Clavinema mariae by Margolis and Moravec. There are no cases of infection with Clavinema mariae in aquaculture fish except for a case of infection with Clavinema mariae in the aquaculture of Sebastes schlegeli in Korea, and all infections were reported on wild fish. In addition, there are no examples of attempts to treat the infections with Clavinema mariae of fish.
The infection itself with Clavinema mariae on the Sebastes schlegeli does not cause direct death of the fish. However, when the fish is infected, it is confirmed that the fish is infected by a secondary pathogenic bacteria through wounds caused when larvae become adults and escape from the life span of the fish, and the infected fish dies. Since the death due to the Clavinema mariae on the west coast of Cheonsu Bay area was first reported in 2012, the deaths due to the Clavinema mariae continuously occur in the summer season, causing serious damage.
Under these technical backgrounds, the present inventors have made intensive efforts to develop an anthelmintic having secured safety capable of exterminating the infection with Clavinema mariae on the Sebastes schlegeli. As a result, it was confirmed that among various candidate materials, Ivermectin was particularly safe for fish and had an excellent exterminating effect, and completed the present invention.